1. Field of the Invention
The invention relates to a resonator shell construction, comprising at least two metallic shell modules connected to each other to form a modular shell construction, each module enclosing at least one resonator cavity.
Resonator constructions are used for implementing high-frequency circuits, for instance in base stations of mobile phone networks. Resonators can be used, for example, as interface and filtering circuits in the amplifiers of transmitter and receiver units in base stations. If the resonator construction comprises several portions, i.e. several resonator cavities, the resonant circuits are connected to one another in such a manner that the resonator construction provides the desired frequency response in the frequency band. This is called sub-band division, in which each resonator cavity covers its own part of the frequency band.
2. Description of the Prior Art
There are several different types of resonators, for example coaxial resonators, helix resonators and cavity resonators. All these three resonator types comprise a metallic shell construction. In coaxial resonators and helix resonators, the shell envelops a conductor which is positioned in the middle of the shell and which can be called, for example, a resonator pin or a resonator conductor. Cavity resonators comprise only a resonator shell.
Resonator shell constructions and individual shell modules for them have been manufactured in many different ways, for instance by bending a thin metal sheet or by milling a solid material. In addition, it is known to manufacture shell modules with one or two cavities by extrusion or die casting. Extrusion, for example, is a good manufacturing method, as it allows the production of long cavity profiles, which are cut into pieces of suitable length, depending on the desired depth of a single cavity.
When the frequency response is to be formed from several portions, it is necessary to use shell constructions comprising several cavities. Shell constructions with several cavities are formed by connecting several shell modules comprising one or more cavities to each other. The properties of a shell construction comprising several cavities--for example, the coupling between Juxtaposed resonator cavities or the resonator conductors in them--can be adjusted by machining the wall between juxtaposed cavities so as to make it lower. The known modular shell constructions are quite simple, since they consist of rectangular shell modules which are connected directly to each other and which are positioned successively or side by side so that the lateral walls of the shell modules are placed against each other. Particular drawbacks of such a construction are the wall between the shell modules, the thickness of the wall, its soldering, and the connection between the modules. If the shell construction, for example, consists of two 2-cavity modules to be juxtaposed, the wall between the modules becomes twice as thick as the wall of a single module; therefore it is more difficult and takes more time to machine the wall between two modules. As stated above, the machining is necessary for adjusting the coupling between the resonator cavities. The different thicknesses of the resonator walls also have a detrimental effect on the electrical behaviour of the resonator, and thus complicate the manufacture of a modular multi-cavity resonator which provides the desired frequency response. The problem with the known shells made by bending a sheet-like material is the need for a large number of soldered joints; a shell construction made from a sheet-like material requires soldered joints not only at the connection between the modules but also within the modules at the points where two different sheet portions are connected to each other.
U.S. Pat. No. 4,087,768 discloses a shell construction consisting of U-shaped portions and separate end portions. However, the separate portions of the construction do not enclose any cavities. The construction is also difficult to assemble.